Because of their relatively light weight and high strength, ceramic materials are widely used to make reinforcing fibers in a variety of composite applications. Such ceramic reinforcing fiber materials include various glasses and other inorganic materials exhibiting the properties desired for the resulting composite. Unfortunately, these ceramic materials are usually very crack sensitive. That is, the stress needed to cause a crack to propagate through a typical ceramic reinforcing fiber material, such as glass, is relatively low. Cracks can initiate from scratches or other imperfections formed on the surface of the ceramic reinforcing material. Glass reinforcing fibers are particularly susceptible to moisture induced cracking. Once a crack is formed, it usually propagates quickly through the ceramic material and can cause the reinforcing fiber to fail prematurely at relatively low applied stresses. This premature failure can significantly deteriorate the mechanical properties of the composite product or article made with such ceramic fibers.
In an effort to protect glass reinforcing fibers from moisture induced and other types of cracking, the surface of the each fiber is usually coated with a layer of some type of protective material, such as a conventional polymeric size, after the fibers are formed. However, the use of such a protective coating is not always as effective as desired. En addition, the step of coating the fibers with such a protective layer increases the costs associated with manufacturing the reinforcing fibers and ultimately the cost of the composite.
Therefore, there is a need for a more effective way to protect glass and other ceramic reinforcing fibers from premature failure due to crack formation and propagation. There is a further need for a less expensive way to protect the ceramic reinforcing fibers without having to coat the surface of each fiber with as thick a layer or with any Layer of some type of protective material, such as a conventional polymeric size or other chemical treatment.